Method for the production of foils from elastomeric material

ABSTRACT

A method for producing elastomeric foils by continuously impregnating a non-woven fabric with a resinous composition in liquid form selected from the group consisting of (a) a resin based on polyhydroxy compounds or polyamines or mixtures thereof and polyisocyanates, (b) resins based or polyhydroxy compounds or polyamines or polycarboxyl compounds or mixtures thereof and polyepoxides and (c) an impregnating mixture based on rubber latex, drying and curing the impregnated fabric freely suspended in hot air and removing the dried foil which is useful as an intermediate layer in the bonding of objects with a high E-molulus and the bonded object per se.

TECHNICAL FIELD

The invention concerns a method for the production of foils ofelastomeric material, as well as the use of these foils in bondingobjects with a high E-modulus, particularly parts in the manufacture ofskis, where the foil is inserted as an intermediate layer, which has theeffect of reducing the shearing forces which can appear in the adhesivejoint during the elastic deformation of the parts bonded to each other,hence particularly in ski production.

STATE OF THE ART

In the bonding of parts with a high E-modulus it is known to insert arubber foil into the adhesive joint. This is done preferably by coatingthe surfaces to be joined with each other, as well as the surfaces ofthe rubber foil with an adhesive that hardens when heated, and then,after inserting the rubber foil as an intermediate layer between thesurfaces to be joined with each other, bonding the whole by theapplication of pressure and heat supply.

In a ski manufacturing method, where a bonding method of this type canbe used with advantage, the skis are produced first from at leastsubstantially plate-shaped parts which are bonded with each other.

The deformations to be absorbed by the adhesive joints, when such a skiis stressed for bending, are generally the greater the more rigid thematerial of the parts to be bonded with each other is, and the shearingforces appearing in the adhesive joint are the greater, the greaterthese deformations are or the thinner the adhesive joints are. The knownmethod for bonding two parts has the effect that these shearing forcesremain within certain limits. The deformation appearing in the bondedzone under bending stress is now absorbed substantially by theintermediate rubber layer. The effect of these intermediate rubberlayers is described in detail in Austrian patent application Ser. No.351,416 of the applicant.

The use of these intermediate rubber layers in the bonding of parts witha high E-modulus is not without problems in practice. First of all, inorder to obtain the quality and uniformity of the adhesive joint, therubber foil used as an intermediate layer should have a thickness ofabout 0.1 to 0.2 mm with a possibly low thickness tolerance. Rubberfoils in this thickness range are very difficult to produce, however,and only with a relatively high thickness tolerance. Thus, e.g. rubberfoils with a thickness of 0.13 mm can only be obtained with a thicknesstolerance of ±0.03 mm, and the quality that can be achieved when theyare used as intermediate layers in adhesive joints is therefore limited.Besides, these rubber foils must be subjected additionally to a specialsurface treatment by wet-chemical methods to obtain a good adhesion inbonding their surfaces.

DESCRIPTION OF THE INVENTION

The invention is based on the problem of providing a method for themanufacture of foils of elastomeric material where the foils can beproduced with a lower thickness tolerance than rubber foils and requireno surface treatment to increase their adhesive power.

The problem underlying the invention is solved by the method for theproduction of foils of elastomeric material according to the invention,which is characterized in that

a. resins based on polyisocyanates and polyhydroxy-compounds and/orpolyamines, or

b. resins based on polyepoxide compounds and polyhydroxy-compoundsand/or polyamines and/or polycarboxyl compounds, or

c. an impregnating mixture based on rubber latex

are applied in liquid form in a continuous process on a unwoven fabric,which can preferably be a tangled unwoven fabric, and that the unwovenfabric passes through a zone of elevated temperature where the resins orthe impregnating mixture harden and/or dry in foil form to an elastomer,containing the fibers of the unwoven fabric. The resins used in liquidform can be present with advantage in the form of dispersions.

According to an advantageous embodiment of the method according to theinvention, when resins based on polyisocyanates are used, these resinsare reactive resins of at least one polyisocyanate components and onepolyhydroxy-component, which can contain preferably a preliminaryproduct of polyisocyanates and polyhydroxy-compounds. At least one ofthe polyhydroxy-compounds used in the preparation has the formula##STR1## where A denotes one of the groups --CH₂ -- or >C═O and (m+q)assumes the values 4 to 30. In the meaning of A=--CH₂ --, n can assumewith advantage the value 3, p the value 4, and (m+q) the values 6 to 30,and in the meaning of A=>C═O, n can assume the value 4, p the values 2to 6, and (m+q) the values 4 to 20.

According to another advantageous embodiment of the method according tothe invention, when using an impregnating mixture based on rubber latex,this mixture can contain a carboxylated styrene-butadiene-latex and, ifnecessary, additionally a vulcanizing agent which can be preferably aformaldehyde condensation product. The solid content of the formaldehydecondensation product used in the mixture can be preferably 5 to 30% byweight.

In another advantageous embodiment of the method according to theinvention, the impregnating mixture contains additionally a naturalrubber latex, where the solid ratio of styrene-butadiene-latex tonatural rubber latex is preferably between 1:2 and 2:1.

It was found that foils with a thickness of 0.1 to 0.2 mm can beproduced with the method according to the invention with a relativelylow thickness tolerance of ±10%. This is due to the fact that theunwoven fabrics used have an absorption power which is uniform overtheir entire surface, and the resin or impregnating mixture, which is inliquid form, can be applied evenly by means of known proven methods,e.g. by impregnation or brushing. The resins or impregnating mixturesaccording to the invention are not sticky without special additives, aslong as they are in liquid form, which has the result that theapplication of the liquid resin on the bonded fabric presents noproblem. The solid elastomer formed is only sticky in the partlyhardened or dried state, that is, while the unwoven fabric laden withthe resin or impregnating mixture passes through the zone of elevatedtemperature, hence during its passage through a continuous furnace.During this passage, the unwoven fabric can be conducted contact-free,e.g. suspended on an air cushion. This way technical problems, which canbe caused by the stickiness of the drying or hardening elastomer, areavoided in a simple manner.

In the finished foil, the fibers of the unwoven fabric no longer form acontinuous matrix, so that they do not decisively alter the mechanicalproperties of the elastomer.

The invention also concerns the use of the foil of elastomeric materialobtained with the method according to the invention, which ischaracterized in that the foil, which has a thickness tolerance of ±10%,is arranged as an intermediate elastomer layer in the adhesive jointwhen bonding two parts with a high E-modulus.

The best way for realizing the invention

For the production of the foil we start from a tangled unwoven cottonfabric in web form, which is withdrawn continuously over a windingmandrel and then conducted over guide rollers through a tank containingthe impregnating resin or impregnating mixture, and subsequently througha pair of squeezing rolls to calibrate the resin coat.

When using an impregnating resin, the composition of which will bedescribed below in three examples, this impregnating resin haspreferably an impregnating viscosity in the range of 10,000 to 100,000mPa, the optimum viscosity value depending on the gross density of thetangled unwoven fabric used, and which can be adjusted, if necessary, bythe addition of a suitable non-reactive solvent.

When using an impregnating mixture based on rubber latex, which ispresent in the form of an aqueous dispersion, and for the composition ofwhich two formulas are given below, this impregnating mixture haspreferably an impregnating viscosity of 50 to 500 mPa, where the optimumviscosity value--similar as with the use of impregnating resins-dependson the gross density of the tangled non-woven fabric and can beadjusted, if necessary, by the addition of water.

After passing through the impregnating plant and the squeezing rolls,the impregnated web enters a hot air shaft in which is passes freelysuspended through several separately controlled heating zones, and atthe end of which it is withdrawn as a non-sticky foil web, and thenwound as an endless band.

The following table contains for different thicknesses of the foil to beproduced the quality of the non-woven fabric used and of the resin-orimpregnating coat (in percent of the gross weight of the fabric, andcalculated in the dried and/or hardened state).

    ______________________________________                                        Foil thickness                                                                           Tangled non-woven cotton fabric                                                                   Coat                                           in mm      weight in g/m.sup.2 %                                              ______________________________________                                        0.15       18                  ab. 400                                        0.20       26                  ab. 650                                        0.25       26                  ab. 900                                        ______________________________________                                    

Here are the five preferred impregnating resin formulas:

1. For the production of a solvent-free impregnating resin, apreliminary product is prepared from (all values are in parts by weight)

66 parts diphenylmethane-4,4'-diisocyanate as a technical crude product(NCO-content ab. 31%) (bought under the tradename Desmodur VL by BAYER)and

200 parts of a linear polyether containing hydroxyl groups with anaverage molar weight of 2000 and an OH-content of 1.7% (bought under thetrade name Desmophen 1900U by BAYER) with

0.6 parts zinc octate as a catalyst to which 7 parts 1,4-butanediol areadded at room temperature.

The gelling time of the impregnating resin thus produced is more than 4hours at room temperature.

2. For the production of an impregnating resin, a mixture is formed atroom temperature which consists of (in parts by weight)

212 parts of a 67% solution of a preliminary product oftrimethylolpropane-toluylenediisocyanate with a NCO-content of about11.5% and an equivalent weight of about 262 in ethylglycol acetate as asolvent (bought under the tradename Desmodur by BAYER),

98 parts of a branched polyether ester containing hydroxyl groups withcontent of about 5% OH and an equivalent weight of about 340 (boughtunder the tradename Desmophen 1150 by BAYER),

245 parts of a linear polyester containing hydroxyl groups with acontent of about 1.7% OH and an average molar weight of about 2000(bought under the tradename Desmophen 1652 by BAYER), as well as

0.5 parts N-methylmorpholine as a catalyst.

The impregnating resin thus prepared has a gelling time of more than 12hours at room temperature.

3. For the production of an impregnating resin, a mixture of (in partsby weight)

66 parts polytetrahydrofuran (molar weight ab. 650) as apolyhydroxy-component,

33.3 parts isophorone diisocyanate

6.3 parts 1,3-butanediol

20 parts ethylglycol acetate and

0.03 parts dibutyl-tin-dilaurate

was heated under constant stirring to 75 deg. C., and the stirring wascontinued until the polyaddition reaction was completed (disappearanceof the NCO-conent), and then cooled.

The impregnating resin obtained by adding to this mixture 25.3 parts ofa technical trimethylol-toluylene diisocyanate adduct in the form of a67% solution in ethylglycol acetate.

The gelling time of the impregnating resin thus produced is more than 6hours at room temperature.

4. For the production of the impregnating resin were mixed (in parts byweight)

41.5 parts polycaprolactone (molar weight ab. 830) as apolyhydroxy-component, and

20 parts ethylglycol acetate

to obtain a clear solution.

The impregnating resin is then obtained by adding to this solution

42 parts of a trimethylol propane-isophorone-diisocyanate adduct in theform of a 70% solution in ethylglycol acetate

The gelling time of this impregnating resin is more than 8 hours at roomtemperature.

5. The impregnating resin consists of a mixture produced at roomtemperature of (in parts by weight)

100 parts of a copolymer of butadiene-acrylonitrile containing carboxylend groups, with an average molar weight of 3300 and a carboxylfunctionality of ab. 1.8

12 parts glycerin triglycide ether with an epoxide equivalent of ab.120-140,

0.5 parts 2,4,6-tris-(dimethylaminomethyl)-phenol

20 parts furnace soot

40 parts toluene as a solvent.

This impregnating resin has a gelling time of more than 24 hours at roomtemperature.

Here are two preferred formulas for impregnating mixtures based onrubber latex.

6. For the production of an impregnating mixture based on rubber latexare mixed (in parts by weight)

100 parts (related to the dry substance) of a carboxylatedbutadiene-styrene-copolymer latex with a styrene portion of 45% and acarboxylic acid portion of 3% by weight in the copolymer, and

30 parts (related to solid resin) of a methyl-etherifiedmelamine-formaldehyde-resin whose melamine-formaldehyde ratio is 1:3.1,where the total portion of dry substance is set to about 55% by weight.

The stability of this impregnating mixture in storage is about 12 hours.

7. In a preferred variant of this impregnating mixture according toformula 6, are added

65 to 260 parts (related to the rubber dry substance) of a 60%centrifuged commercial available natural latex stabilized with 0.7%ammonia.

With this addition of natural latex, the mechanical toughness of theresulting elastomer can be increased or adjusted to the desired valuewithin a wide range.

Industrial utilization

The foils produced with the method according to the invention are usedfor bonding, particularly in metal-metal bonding, and especially in themanufacture of skis, where they are inserted as intermediate layers inthe adhesive joints. If commercial adhesives on an epoxide resin baseare used, the bonding qualities are good and very uniform. Drum peelingtests according to DIN 53295 show high peel strength values.

We claim:
 1. A method of producing elastomeric foils comprisingcontinuously impregnating a non-woven fabric with a resinous compositionin liquid form selected from the group consisting of (a) a resin basedor polyhydroxy compounds or polyamines or mixtures thereof andpolyisocyanates, (b) resins based on polyhydroxy compounds or polyaminesor polycarboxyl compounds or mixtures thereof and polyepoxides and (c)an impregnating mixture based on rubber latex to form a sticky foil,drying and curing the impregnated fabric in the form of a sticky foilfreely suspended in hot air and removing the dried non-sticky,elastomeric foil.
 2. The method according to claim 1, characterized inthat a tangled bonded cotton fabric is used as said unwoven fabric. 3.The method according to claim 1, characterized in that said resinousmixture used in liquid form are present in the form of dispersions. 4.The method according to claim 1, characterized in that, when resinsbased on polyisocyanates are used, these resins are reactive resins ofat least one polyisocyanate component or one polyhydroxy component. 5.The method according to claim 4, characterized in that at least one ofthe polyhydroxy components used in the preparation of the resin has astructure of the formula ##STR2## where A denotes one of the groups--CH₂ or >C═O, and (m+q) assumes the values 4 to
 30. 6. The methodaccording to claim 5, characterized in that when A=--CH₂ --, n assumesthe value 3, p the value 4, and (m+q) the values 6 to
 30. 7. The methodaccording to claim 5, characterized in that when A=>C═O, n assumes thevalue 4, p the values 2 to 6, and (m+q) the values 4 to
 20. 8. Themethod according to claim 1, characterized in that the reactive resinscontain at least one preliminary product of polyisocyanates andpolyhydroxy-compounds.
 9. The method according to claim 1, characterizedin that, when an impregnating mixture based on a rubber latex is used,this mixture contains a carboxylated styrene-butadiene-latex.
 10. Themethod according to claim 9, characterized in the impregnating mixtureused contains additionally a vulcanizing agent.
 11. The method accordingto claim 10, characterized in that said vulcanizing agent is aformaldehyde condensation product.
 12. The method according to claim 11,characterized in that the solid content of the formaldehyde condensationproduct used in the impregnating mixture is 5 to 30% by weight.
 13. Themethod according to claim 1, characterized in that said impregnatingmixture contains additionally a natural rubber latex.
 14. The methodaccording to claim 13, characterized in that the solid ratiostyrene-butadiene-latex to natural rubber latex is between 1:2 and 2:1.15. Foil of elastomeric material, characterized in that it is producedaccording to claim 1.